This species is known from material discovered in Aramis, Ethiopia, in the Middle Awash region at locality ARA-VP-6/500. The material was first described in 1994 by Tim White and two of his students (now professional paleoanthropologists), G. Suwa and B. Asfaw (White et al. 1994). This site has yielded material from over 50 individuals so far, which dates to approximately 4.4 mya. Most of the remains are dental (e.g. ARA-VP-1/129), but there are cranial and postcranial fragments, as well as much of a particular postcranial skeleton. As of now, the material seems to be the oldest taphonomically determined example of australopithecines (material such as the LT 329, and material from the Chemeron Formation near Baringo date older but are very fragmentary and not well described). Initially determined as a new species of australopithecine, the discoverers later argued for a new genus, Ardipithecus, however, the material has not been published extensively and the naming of a new species is always contested (much less a new genus!). It is safe to refer to the species as Australopithecus ramidus for the time being, until adequate proof for a genus is explicated.

One aspect that is particularly important about this species is the environment in which it was found. Unlike the open savanna that was hypothesized in many theories of hominid origins, the material was found in strata with preserved fossil woods and seeds as well as a predominance of colobine monkeys in the faunal remains. Also, savanna-associated megafauna are rare, indicating that this species lived in a wooded environment. This is important because this species was fully bipedal; the particulars of which will be discussed in a later section.

The neurocranium pieces (such as ARA-VP 1/125 and ARA-VP 1/500) show features that are similar to modern chimpanzees - *note* modern chimpanzees are not good referents for a common ancestor of modern humans and the African apes, but is being compared since the morphological features are due to differences in brain size and things like tooth loading that work similarly in most mammals in developmental anatomy. For example, the spongy bone on the temporal that is pneumatized extends into the temporal squama. The external auditory meatus is small, and the mandibular fossa is flat. The morphology seems to indicate heavy anterior tooth loading, which indicates regular use of the front teeth in clamping and pulling. This could be indicative of aggressive biting, or more likely, leaf stripping - which would be an important adaptive behavior in their woodland environment.

Some portions of the basicranium are preserved (occipital and temporal portions), and they provide some important information. The occipital condyles are as small as the smallest known australopithecine adults, which indicates a very small size for the specimen (ARA-VP 1/500). The size of the condyles corresponds to the force exerted by nuchal muscles, which is correlated to body size. Also, the position of the foramen magnum is very anterior to the cranial base, similar to the placement in other australopithecines. This feature, along with a deep digastric sulcus indicating a shortened cranial base, strongly indicate that A. ramidus held its head upright like other australopithecines.

The available postcranial evidence seems to indicate that A. ramidus was an obligate biped. (This is also supported by the position of the foramen magnum.) The humeri, radii, and ulni show that the species had very powerful arms and forearms, which were not used to support body weight (they weren't quadrapeds), and which closely resemble modern human and large-bodied apes. The forearm features indicate that it was used in climbing (the increased strength and robusticity due to the loss of grasping feet and the need to make up for weight load in climbing). Much more postcranial material from a single skeleton (45% complete) found in 1995 may give more insight, but the material has not been published as of yet.

Much of the material is dental, and more is known about the dentition of the species than about the postcranial material. Distinctive features of A. ramidus, as opposed to either chimpanzee or later australopithecines like A. afarensis include:

• Canines with thickened enamel relative to the chimpanzee condition.
• Upper canines are broad as opposed to chimps.
• Postcanine megadontia (bigger than chimps, but not as big as later australopithecines).
• The incisors are small relative to the molars (anterior tooth size reduction begins).
• The M₃s are large and elongated.
• The dm₁ lacks a honing facet for the upper canine (no sectorial tooth).
• The P₃ is small relative to post P₃ dentition.
• The upper and lower canines are bigger than afarensis
• Absolutely and relatively thin enamel relative to afarensis.
• The M³s are assymetrical with dominant buccal cusps relative to afarensis.

It is also important to not that unlike afarensis, ramidus seems to lack an articular eminence on the TMJ.

The Aramis discoveries are important for several reasons. First, they place very early hominids in a woodland setting rather than a savanna one. Second, They show that although there is an emphasis on anterior loading, an adaptive trend emphasizing powerful mastication had begun. Also, they establish a unique link with chimpanzees based on cranial, dental, and postcranial similarities. It is also important to note that ramidus were almost contemporaries with afarensis (and might have been). Since the two species are adapted to different ecological environments, there are major differences between the two species, but some features both have seem to indicate that the common ancestor of humans and chimpanzees was probably more hominid-like than chimpanzee-like. A conclusion that is gaining support, in opposition to the presupposition that the common ancestor was more chimpanzee-like. In short, this is a very new species that is changing some ideas of modern human origins. It will be interesting to see the impact the material makes once it is extensively published and disseminated.

This bibliography contains the sources of the information cited above, as well as any sources that could provide any other information on the subject. If you know of any other sources that are pertinent to A. ramidus, please e-mail me the citation in the format used below, and I will add it. Any problems with information I presented above can be sent to me here. I don't want to provide misinformation, and any corrections are gladly accepted (with proper documentation of what is wrong and why, with sources). Thanks!

Aiello, L.C. 1992. "Allometry and the analysis of size and shape in human evolution." In Journal of Human Evolution, vol. 22 no.2, pp.127-147.

Day, M. 1995. "Remarkable delay." In Nature, vol. 376. pg.111.

Kalb, J., C. Jolly, E. Oswald, and P. Whitehead. 1984. "Early hominid habitation in Ethiopia." In American Scientist, vol. 72, pp. 168-178.

Kappelman, J., and J. Fleagle. 1995. "Age of early hominids." In Nature, vol. 376, pp. 558-559.

Johanson, D. and B. Edgar. 1996. From Lucy to Language. New York: Simon and Schuster Editions.

White, T., G. Suwa, and B. Asfaw. 1994. "Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia." In Nature, vol. 371. pp. 306-312.

White, T., G. Suwa, and B. Asfaw. 1995. "Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia." In Nature, vol. 375, pg. 88.

WoldeGabriel, G. T. White, G. Suwa, P. Renne, J. de Heinzelin, W. Hart, and G. Heiken. 1994. Ecological and temporal placement of early Pliocene hominids at Aramis, Ethiopia." In Nature, vol. 371. pp. 330-333.

Wolpoff, M. 1999. Paleoanthropology. second edition. Boston: McGraw-Hill.